Temperature sensor assemblies for electric warming blankets

ABSTRACT

An electric warming blanket for warming patients during surgery and other medical procedures includes a flexible heater and a temperature sensor assembly coupled thereto; a first layer of water resistant material coupled to a second layer of water resistant material, about a perimeter of the heater, forms a substantially hermetically sealed space for the heater and the temperature sensor assembly. The blanket may further include a thermal insulation layer disposed between the temperature sensor assembly and the first layer of water resistant material. The temperature sensor assembly may provide input of an average temperature over a portion of a surface area of the heater to a temperature controller, when the heater and sensor assembly are coupled to the controller.

PRIORITY CLAIM

The present application claims priority to co-pending provisionalapplications Ser. No. 60/825,573, entitled HEATING BLANKET SYSTEM filedon Sep. 13, 2006; Ser. No. 60/722,106, entitled ELECTRIC WARMING BLANKETINCLUDING TEMPERATURE ZONES AUTOMATICALLY OPTIMIZED, filed Sep. 29,2005; and Ser. No. 60/722,246, entitled HEATING BLANKET, filed Sep. 29,2005; all of which are incorporated by reference in their entiretiesherein.

RELATED APPLICATIONS

The present application is related to the following commonly assignedutility patent applications, all of which are filed concurrentlyherewith and all of which are hereby incorporated by reference in theirentireties: A) ELECTRIC WARMING BLANKET HAVING OPTIMIZED TEMPERATUREZONES, Practitioner docket number 49278.2.5.2; B) NOVEL DESIGNS FORHEATING BLANKETS AND PADS, Practitioner docket number 49278.2.7.2; C)FLEXIBLE HEATING ELEMENT CONSTRUCTION, Practitioner docket number49278.2.15; D) BUS BAR ATTACHMENTS FOR FLEXIBLE HEATING ELEMENTS,Practitioner docket number 49278.2.16; and E) BUS BAR INTERFACES FORFLEXIBLE HEATING ELEMENTS, Practitioner docket number 49278.2.17.

TECHNICAL FIELD

The present invention is related to heating or warming blankets or padsand more particularly to those including electrical heating elements.

BACKGROUND

It is well established that surgical patients under anesthesia becomepoikilothermic. This means that the patients lose their ability tocontrol their body temperature and will take on or lose heat dependingon the temperature of the environment. Since modern operating rooms areall air conditioned to a relatively low temperature for surgeon comfort,the majority of patients undergoing general anesthesia will lose heatand become clinically hypothermic if not warmed.

Over the past 15 years, forced-air warming (FAW) has become the“standard of care” for preventing and treating the hypothermia caused byanesthesia and surgery. FAW consists of a large heater/blower attachedby a hose to an inflatable air blanket. The warm air is distributed overthe patient within the chambers of the blanket and then is exhaustedonto the patient through holes in the bottom surface of the blanket.

Although FAW is clinically effective, it suffers from several problemsincluding: a relatively high price; air blowing in the operating room,which can be noisy and can potentially contaminate the surgical field;and bulkiness, which, at times, may obscure the view of the surgeon.Moreover, the low specific heat of air and the rapid loss of heat fromair require that the temperature of the air, as it leaves the hose, bedangerously high —in some products as high as 45° C. This posessignificant dangers for the patient. Second and third degree burns haveoccurred both because of contact between the hose and the patient'sskin, and by blowing hot air directly from the hose onto the skinwithout connecting a blanket to the hose. This condition is commonenough to have its own name—“hosing.” The manufacturers of forced airwarming equipment actively warn their users against hosing and the risksit poses to the patient.

To overcome the aforementioned problems with FAW, several companies havedeveloped electric warming blankets. However, there is still a need forelectrically heated blankets or pads that can be used safely andeffectively warm patients undergoing surgery or other medicaltreatments. These blankets need to be flexible in order to effectivelydrape over the patient (making excellent contact for conductive heattransfer and maximizing the area of the patient's skin receivingconductive as well as radiant heat transfer), and should incorporatemeans for precise temperature control.

Precise temperature control is important because non-uniform heatdistribution can occur within an electric warming blanket.Unfortunately, many temperature sensors used to provide feedback to atemperature controller do not dependably report an accurate averagetemperature of the blanket because they sense temperature from too smallof an area. For example, if the temperature of a measured location iscooler than the average blanket temperature, the temperature sensor willcause the controller to deliver more power to the heater and theresulting average temperature of the heater will be higher than desired.

Further, an electric blanket can overheat if the temperature sensor isthermally grounded to a cool object. This condition can occur if a coolobject such as a metal pan is placed on top of the heater in the area ofthe temperature sensor. The sensor “feels” cool and tells thetemperature controller to deliver more power to the heater.

Accordingly, there is a need for a blanket that utilizes a temperaturesensor that takes temperature measurements that are representative ofthe average temperature of the blanket. Further, there is a need for ablanket with a temperature sensor that will not cause the blanket tooverheat if a cool object is placed in proximity to it. Variousembodiments of the invention described herein solve one or more of theproblems discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of thepresent invention and therefore do not limit the scope of the invention.The drawings are not to scale (unless so stated) and are intended foruse in conjunction with the explanations in the following detaileddescription. Embodiments of the present invention will hereinafter bedescribed in conjunction with the appended drawings, wherein likenumerals denote like elements.

FIG. 1A is a plan view of a flexible heating blanket subassembly for aheating blanket, according to some embodiments of the present invention.

FIGS. 1B-C are end views of two embodiments of the subassembly shown inFIG. 1A.

FIG. 1D is a schematic showing a blanket including the subassembly ofFIG. 1A draped over a body.

FIG. 2A is a top plan view of a heating element assembly, according tosome embodiments of the present invention, which may be incorporated inthe blanket shown in FIG. 3A.

FIG. 2B is a section view through section line A-A of FIG. 2A.

FIG. 2C is an enlarged plan view and corresponding end view schematic ofa portion of the assembly shown in FIG. 2A, according to someembodiments of the present invention.

FIG. 2D is an enlarged view of a portion of the assembly shown in FIG.2A, according to some embodiments of the present invention.

FIG. 3A is a top plan view, including partial cut-away views, of a lowerbody heating blanket, according to some embodiments of the presentinvention.

FIG. 3B is a schematic side view of the blanket of FIG. 3A draped over alower body portion of a patient.

FIG. 3C is a top plan view of a heating element assembly, which may beincorporated in the blanket shown in FIG. 3A.

FIG. 3D is a cross-section view through section line D-D of FIG. 3C.

FIG. 4A is a plan view of flexible heating element, according to somealternate embodiments of the present invention.

FIG. 4B is a top plan view, including a partial cut-away view, of aheating element assembly, according to some embodiments of the presentinvention, which may be incorporated in the blanket shown in FIG. 4C.

FIG. 4C is a top plan view, including a partial cut-away view, of anupper body heating blanket, according to some embodiments of the presentinvention.

FIG. 4D is a schematic end view of the blanket of FIG. 4B draped over anupper body portion of a patient.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical illustrations for implementing exemplary embodiments of thepresent invention. Examples of constructions, materials, dimensions, andmanufacturing processes are provided for selected elements, and allother elements employ that which is known to those of skill in the fieldof the invention. Those skilled in the art will recognize that many ofthe examples provided have suitable alternatives that can be utilized.The term ‘blanket’, used to describe embodiments of the presentinvention, may be considered to encompass heating blankets and pads.

FIG. 1A is a plan view of a flexible heating blanket subassembly 100,according to some embodiments of the present invention; and FIGS. 1B-Care end views of two embodiments of the subassembly shown in FIG. 1A.FIG. 1A illustrates a flexible sheet-like heating element, or heater, 10of subassembly 100 including a first end 101, a second end 102, a firstlateral portion 11 extending between ends 101, 102, and a second lateralportion 12, opposite first lateral portion 11, also extending betweenends 101, 102. According to preferred embodiments of the presentinvention, heater 10 comprises a conductive fabric or a fabricincorporating closely spaced conductive elements such that heater 10 hasa substantially uniform watt density output, preferably less thanapproximately 0.5 watts/sq. inch, and more preferably betweenapproximately 0.2 and approximately 0.4 watts/sq. inch, across a surfacearea, of one or both sides 13, 14 (FIGS. 1B-C), the surface areaincluding and extending between lateral portions 11, 12 of heater 10.Some examples of conductive fabrics which may be employed by embodimentsof the present invention include, without limitation, carbon fiberfabrics, fabrics made from carbonized fibers, woven or non-wovennon-conductive substrates coated with a conductive material, forexample, polypyrrole, carbonized ink, or metalized ink.

FIG. 1A further illustrates subassembly 100 including two bus bars 15coupled to heating element 10 for powering element 10; each bar 15 isshown extending alongside opposing lateral portions 11, 12, betweenfirst and second ends 101, 102. With reference to FIG. 1B, according tosome embodiments, bus bars 15 are coupled to heating element 10 withinfolds of opposing wrapped perimeter edges 108 of heating element 10 by astitched coupling 145, for example, formed with conductive thread suchas silver-coated polyester or nylon thread (Marktek Inc., Chesterfield,Mo.), extending through edges 108 of heating element 10, bars 15, andagain through heating element 10 on opposite side of bars 15. Accordingto alternate embodiments heating element 10 is not folded over bus bars15 as shown. Alternative threads or yarns employed by embodiments of thepresent invention may be made of other polymeric or natural fiberscoated with other electrically conductive materials; in addition,nickel, gold, platinum and various conductive polymers can be used tomake conductive threads. Metal threads such as stainless steel, copperor nickel could also be used for this application. According to anexemplary embodiment, bars 15 are comprised of flattened tubes ofbraided wires, such as are known to those skilled in the art, forexample, a flat braided silver coated copper wire, and may thusaccommodate the thread extending therethrough, passing through openingsbetween the braided wires thereof. In addition such bars are flexible toenhance the flexibility of blanket subassembly 100. According toalternate embodiments, bus bars 15 can be a conductive foil or wire,flattened braided wires not formed in tubes, an embroidery of conductivethread, or a printing of conductive ink. Preferably, bus bars 15 areeach a flat braided silver-coated copper wire material, since a silvercoating has shown superior durability with repeated flexion, as comparedto tin-coated wire, for example, and may be less susceptible tooxidative interaction with a polypyrrole coating of heating element 10according to an embodiment described below. Additionally, an oxidativepotential, related to dissimilar metals in contact with one another isreduced if a silver-coated thread is used for stitched coupling 145 of asilver-coated bus bar 15.

According to an exemplary embodiment, a conductive fabric comprisingheating element 10 comprises a non-woven polyester having a basis weightof approximately 130 g/m² and being 100% coated with polypyrrole(available from Eeonyx Inc., Pinole, Calif.); the coated fabric has anaverage resistance, for example, determined with a four point probemeasurement, of approximately 15-20 ohms per square inch at about 48volts, which is suitable to produce the preferred watt density of 0.2 to0.4 watts/sq. in. for surface areas of heating element 10 having awidth, between bus bars 15, in the neighborhood of about 20 inches. Sucha width is suitable for a lower body heating blanket, some embodimentsof which will be described below. A resistance of such a conductivefabric may be tailored for different widths between bus bars (widerrequiring a lower resistance and narrower requiring a higher resistance)by increasing or decreasing a surface area of the fabric that canreceive the conductive coating, for example by increasing or decreasingthe basis weight of the fabric. Resistance over the surface area of theconductive fabrics is generally uniform in many embodiments of thepresent invention. However, the resistance over different portions ofthe surface area of conductive fabrics such as these may vary, forexample, due to variation in a thickness of a conductive coating,variation within the conductive coating itself, variation in effectivesurface area of the substrate which is available to receive theconductive coating, or variation in the density of the substrate itself.Local surface resistance across a heating element, for example heater10, is directly related to heat generation according to the followingrelationship:Q (Joules)=I ²(Amps)×R(Ohms)

Variability in resistance thus translates into variability in heatgeneration, which is measured as a temperature. According to preferredembodiments of the present invention, which are employed to warmpatients undergoing surgery, precise temperature control is desirable.Means for determining heating element temperatures, which average outtemperature variability caused by resistance variability across asurface of the heating element, are described below in conjunction withFIGS. 2A-B.

A flexibility of blanket subassembly 100, provided primarily by flexibleheating element 10, and optionally enhanced by the incorporation offlexible bus bars, allows blanket subassembly 100 to conform to thecontours of a body, for example, all or a portion of a patientundergoing surgery, rather than simply bridging across high spots of thebody; such conformance may optimize a conductive heat transfer fromelement 10 to a surface of the body. However, as illustrated in FIG. 1D,heating element 10 may be draped over a body 16 such that lateralportions 11, 12 do not contact side surfaces of body 16; the mechanismof heat transfer between portions 11, 12 and body 16, as illustrated inFIG. 1D, is primarily radiant with some convection.

The uniform watt-density output across the surface areas of preferredembodiments of heating element 10 translates into generally uniformheating of the surface areas, but not necessarily a uniform temperature.At locations of heating element 10 which are in conductive contact witha body acting as a heat sink, for example, body 16, the heat isefficiently drawn away from heating element 10 and into the body, forexample by blood flow, while at those locations where element 10 doesnot come into conductive contact with the body, for example lateralportions 11, 12 as illustrated in FIG. 1D, an insulating air gap existsbetween the body and those portions, so that the heat is not drawn offthose portions as easily. Therefore, those portions of heating element10 not in conductive contact with the body will gain in temperature,since heat is not transferred as efficiently from these portions as fromthose in conductive contact with the body. The ‘non-contacting’ portionswill reach a higher equilibrium temperature than that of the‘contacting’ portions, when the radiant and convective heat loss equalthe constant heat production through heating element 10. Althoughradiant and convective heat transfer are more efficient at higher heatertemperatures, the laws of thermodynamics dictate that as long as thereis a uniform watt-density of heat production, even at the highertemperature, the radiant and convective heat transfer from a blanket ofthis construction will result in a lower heat flux to the skin than theheat flux caused by the conductive heat transfer at the ‘contacting’portions at the lower temperature. Even though the temperature ishigher, the watt-density is uniform and, since the radiant andconvective heat transfer are less efficient than conductive heattransfer, the ‘non-contacting’ portions must have a lower heat flux.Therefore, by controlling the ‘contacting’ portions to a safetemperature, for example, via a temperature sensor 121 coupled toheating element 10 in a location where element 10 will be in conductivecontact with the body, as illustrated in FIG. 1D, the ‘non-contacting’portions, for example, lateral portions 11, 12, will also be operatingat a safe temperature because of the less efficient radiant andconvective heat transfer. According to preferred embodiments, heatingelement 10 comprises a conductive fabric having a relatively smallthermal mass so that when a portion of the heater that is operating atthe higher temperature is touched, suddenly converting a‘non-contacting’ portion into a ‘contacting’ portion, that portion willcool almost instantly to the lower operating temperature.

According to embodiments of the present invention, zones of heatingelement 10 may be differentiated according to whether or not portions ofelement 10 are in conductive contact with a body, for example, a patientundergoing surgery. In the case of conductive heating, gentle externalpressure may be applied to a heating blanket including heating element10, which pressure forces heating element 10 into better conductivecontact with the patient to improve heat transfer. However, if excessivepressure is applied the blood flow to that skin may be reduced at thesame time that the heat transfer is improved and this combination ofheat and pressure to the skin can be dangerous. It is well known thatpatients with poor perfusion should not have prolonged contact withconductive heat in excess of approximately 42° C. 42° C. has been shownin several studies to be the highest skin temperature, which cannotcause thermal damage to normally perfused skin, even with prolongedexposure. (Stoll & Greene, Relationship between pain and tissue damagedue to thermal radiation. J. Applied Physiology 14(3):373-382. 1959 andMoritz and Henriques, Studies of thermal injury: The relative importanceof time and surface temperature in the causation of cutaneous burns. Am.J. Pathology 23:695-720, 1947) Thus, according to certain embodiments ofthe present invention, the portion of heating element 10 that is inconductive contact with the patient is controlled to approximately 43°C. in order to achieve a temperature of about 41-42° C. on a surface aheating blanket cover that surrounds element 10, for example, a cover orshell 20, 40 which will be described below in conjunction with FIGS. 3Aand 4C. With further reference to FIG. 1D, flaps 125 are shown extendinglaterally from either side of heating element 10 in order to enclose thesides of body 16 thereby preventing heat loss; according to preferredembodiments of the present invention, flaps 125 are not heated and thusprovide no thermal injury risk to body if they were to be tucked beneathsides of body 16.

Referring now to the end view of FIG. 1C, an alternate embodiment tothat shown in FIG. 1B is presented. FIG. 1C illustrates subassembly 100wherein insulating members 18, for example, fiberglass material stripshaving an optional PTFE coating and a thickness of approximately 0.003inch, extend between bus bars 15 and heating element 10 at each stitchedcoupling 145, so that electrical contact points between bars 15 andheating element 10 are solely defined by the conductive thread ofstitched couplings 145.

FIG. 2A is a top plan view of a heating element assembly 250, accordingto some embodiments of the present invention, which may be incorporatedby blanket 200, which is shown in FIG. 3A and further described below.FIG. 2B is a section view through section line A-A of FIG. 2A. FIGS.2A-B illustrate a temperature sensor assembly 421 assembled on side 14of heater 10, and heater 10 overlaid on both sides 13, 14 with anelectrically insulating layer 210, preferably formed of a flexiblenon-woven high loft fibrous material, for example, 1.5 OSY (ounces persquare yard) nylon, which is preferably laminated to sides 13, 14 with ahotmelt laminating adhesive. In some embodiments, the adhesive isapplied over the entire interfaces between layer 210 and heater 10.Other examples of suitable materials for layer 210 include, withoutlimitation, polymeric foam, a woven fabric, such as cotton orfiberglass, and a relatively thin plastic film. According to preferredembodiments, overlaid layers 210, without compromising the flexibilityof heating assembly 250, prevent electrical shorting of one portion ofheater 10 with another portion of heater 10 if heater 10 is folded overonto itself. Heating element assembly 250 may be enclosed within arelatively durable and waterproof shell, for example shell 20 shown withdashed lines in FIG. 2B, and will be powered by a relatively low voltage(approximately 48V). Layers 210 may even be porous in nature to furthermaintain the desired flexibility of assembly 250.

FIG. 2C is an enlarged plan view and a corresponding end view schematicshowing some details of the corner of assembly 250 that is circled inFIG. 2A, according to some embodiments. FIG. 2C is representative ofeach corner of assembly 250. FIG. 2C illustrates insulating layer 210disposed over side 14 of heater 10 and extending beneath bus bar 15,optional electrical insulating member 18, and layer 210 disposed overside 13 of heater 10 and terminated adjacent bus bar 15 within lateralportion 12 so that threads of conductive stitching 145 securing bus bars15 to heater 10 electrically contact heating element 10 along side 13 ofheating element 10. FIG. 2C further illustrates two rows of conductivestitching 145 coupling bus bar 15 to heating element 10, and bus bar 15and insulating member 18 extending past end 102.

FIG. 2A further illustrates junctions 50 coupling leads 205 to each busbar 15, and another lead 221 coupled to and extending from temperaturesensor assembly 421; each of leads 205, 221 extend over insulating layer210 and into an electrical connector housing 225 containing a connector23, which will be described in greater detail below, in conjunction withFIGS. 3A-C. FIG. 2D is an enlarged view of junction 50, which is circledin FIG. 2A, according to some embodiments of the present invention. FIG.2D illustrates junction 50 including a conductive insert 55 which hasbeen secured to bus bar 15, for example, by inserting insert 55 througha side wall of bus bar 15 and into an inner diameter thereof. FIG. 2Dfurther illustrates lead 205 coupled to insert 55, for example, viasoldering, and an insulating tube and strain relief 54, for example, apolymer shrink tube, surrounding the coupling between lead 205 andinsert 55.

Returning now to FIG. 2B, temperature sensor assembly 421 will bedescribed in greater detail. FIG. 2B illustrates assembly 421 includinga substrate 211, for example, of polyimide (Kapton), on which atemperature sensor 21, for example, a surface mount chip thermistor(such as a Panasonic ERT-J1VG103FA: 10 K, 1% chip thermistor), ismounted; a heat spreader 212, for example, a copper or aluminum foil, ismounted to an opposite side of substrate 211, for example, being bondedwith a pressure sensitive adhesive; substrate 211 is relatively thin,for example about 0.0005 inch thick, so that heat transfer between heatspreader 212 and sensor is not significantly impeded. Temperature sensorassembly 421 may be bonded to layer 210 with an adhesive layer 213, forexample, hotmelt EVA. Although not shown, it should be noted that sensorassembly 421 may be potted with a flexible electrically insulatingmaterial, such as silicon or polyurethane.

According to the illustrated embodiment, heat spreader 212 is sized tocontact an enlarged surface area so that a temperature sensed by sensor21 is more representative of an average temperature over a region ofheater 10 surrounding sensor 21, which is positioned such that, when aheating blanket including heater 10 is placed over a body, the regionssurrounding sensor 21 will be in conductive contact with the body. Aspreviously described, it is desirable that a temperature ofapproximately 43° C. be maintained over a surface of heater 10 which isin conductive contact with a body of a patient undergoing surgery. Othertypes of heat spreaders, in addition to metallic foils, include metallicmeshes or screens, or an adhesive/epoxy filled with a thermallyconductive material.

Heat spreader 212 is a desirable component of a temperature sensorassembly, according to some embodiments of the present invention, sinceconductive fabrics employed by heating element 10, such as thosepreviously described, may not exhibit uniform resistance across surfaceareas thereof. Heat spreader 212, having a surface area that does notexceed approximately four square inches, according to a preferredembodiment, may be effective in averaging out relatively small scalespatial resistance variation, for example, about 3% to 10% variabilityover less than about one or two inches. Such a limitation on heatspreader 212 surface area may be necessary so that heat spreader 212does not become too bulky, since the larger the surface area, thegreater the thickness of spreader 212 needed in order to maintaineffective heat transfer across spreader 212 and to sensor 21. Inaddition, if spreader 212 is too thick, a thermal mass of spreader 212will cause spreader 212 to respond too slowly to changes in heat loss orgain by heating element. According to an exemplary embodiment of thepresent invention, spreader 212 has a surface area of no greater thanapproximately four square inches and a thickness of no greater thanapproximately 0.001 inch. Some alternate embodiments of the presentinvention address a non-uniform resistance across a surface area ofelement 10 by employing a distributed temperature sensor, for example, aresistance temperature detector (RTD) laid out in flat plane across asurface of heater 10, or by employing an infrared temperaturemeasurement device positioned to receive thermal radiation from a givenarea of heater 10. An additional alternate embodiment is contemplated inwhich an array of temperature sensors are positioned over the surface ofheater 10, being spaced apart so as to collect temperature readingswhich may be averaged to account for resistance variance.

According to a preferred embodiment, assembly 421 includes a second,redundant, temperature sensor mounted to substrate 211, close enough tosensor 21 to detect approximately the same temperature; while sensor 21may be coupled to a microprocessor temperature control, the secondsensor, for example, a chip thermistor similar to sensor 21, may becoupled to an analog over-temperature cutout that cuts power to element10, and/or sends a signal triggering an audible or visible alarm. Thedesign of the second sensor may be the same as the first sensor and neednot be described again. Another safety check may be provided by mountingan identification resistor to substrate 211 in order to detect anincrease in resistance of element 10, due, for example, to degradationof the material of element 10, or a fractured bus bar; the optionalidentification resistor monitors a resistance of heating element 10 andcompares the measured resistance to an original resistance of element10.

According to some embodiments of the present invention, for example asillustrated in FIG. 2A, super over-temperature sensors 41 areincorporated to detect overheating of areas of assembly 250 susceptibleto rucking, that is areas, for example, lateral portions 11, 12, whereassembly 250 is most likely to be folded over on itself, eitherinadvertently or on purpose to gain access to a portion of a patientdisposed beneath a blanket including assembly 250. An area of assembly250 which is beneath the folded-over portion of assembly 250, and not inclose proximity to sensor assembly 421, can become significantly warmerdue to the additional thermal insulation provided by the folded-overportion that goes undetected by sensor 21. According to preferredembodiments, sensors 41 are wired in series, as illustrated in FIG. 2A.Super over-temperature sensors 41 may be set to open, or significantlyincrease resistance in, a circuit, for example, the over-temperaturecircuit, thereby activating an alarm and/or cutting power to heatingelement 10, at prescribed temperatures that are significantly above thenormal operating range, for example, temperatures between approximately45° C. and approximately 60° C. Alternately, sensors 41 may be part ofthe bus bar power circuit, in which case sensors 41 directly shut downpower to heating element 10 when in an open condition or add sufficientresistance when in a high resistance condition to substantially reduceheating of element 10.

FIG. 3A is a top plan view, including partial cut-away views, of a lowerbody heating blanket 200, according to some embodiments of the presentinvention, which may be used to keep a patient warm during surgery. FIG.3A illustrates blanket 200 including heating element assembly 250covered by flexible shell 20; shell 20 protects and isolates assembly250 from an external environment of blanket 200 and may further protecta patient disposed beneath blanket 200 from electrical shock hazards.According to preferred embodiments of the present invention, shell 20 iswaterproof to prevent fluids, for example, bodily fluids, IV fluids, orcleaning fluids, from contacting assembly 250, and may further includean anti-microbial element, for example, being a SILVERion™ antimicrobialfabric available from Domestic Fabrics Corporation. According to theillustrated embodiment, blanket 200 further includes a layer of thermalinsulation 201 extending over a top side (corresponding to side 14 ofheating element 10) of assembly 250; layer 201 may or may not be bondedto a surface of assembly 250. Layer 201 may serve to prevent heat lossaway from a body disposed on the opposite side of blanket 200,particularly if a heat sink comes into contact with the top side ofblanket 200. FIG. 3C illustrates insulation 201 extending over an entiresurface of side 14 of heating element 10 and over sensor assembly 421.According to the illustrated embodiment, layer 201 is secured to heatingelement assembly 250 to form an assembly 250′, as will be described ingreater detail below. According to an exemplary embodiment of thepresent invention, insulating layer 201 comprises a polymer foam, forexample, a 1 pound density 30 ILD urethane foam, which has a thicknessbetween approximately ⅛^(th) inch and approximately ¾^(th) inch.According to alternate embodiments layer 201 comprises any, or acombination of the following: high loft fibrous polymeric non-wovenmaterial, non-woven cellulose material, and air, for example, heldwithin a polymeric film bubble.

FIG. 3A further illustrates shell 20 forming flaps 25 extendinglaterally from either side of assembly 250 and a foot drape 26 extendinglongitudinally from assembly 250. According to exemplary embodiments ofthe present invention, a length of assembly 250 is either approximately28 inches or approximately 48 inches, the shorter length providingadequate coverage for smaller patients or a smaller portion of anaverage adult patient. FIG. 3B is a schematic side view of blanket 200draped over a lower body portion of a patient. With reference to FIG. 3Bit may be appreciated that flaps 25, extending down on either side ofthe patient, and foot drape 26, being folded under and secured byreversible fasteners 29 (FIG. 3A) to form a pocket about the feet of thepatient, together effectively enclose the lower body portion of thepatient to prevent heat loss. With reference to FIG. 2A, in conjunctionwith FIG. 3B, it may be appreciated that temperature sensor assembly 421is located on assembly 250 so that, when blanket 200 including assembly250 is draped over the lower body of the patient, the area of heatingelement 10 surrounding sensor assembly 421 will be in conductive contactwith one of the legs of the patient in order to maintain a safetemperature distribution across element 10.

According to some embodiments of the present invention, shell 20includes top and bottom sheets extending over either side of assembly250; the two sheets of shell 20 are coupled together along a seal zone22 (shown with cross-hatching in the cut-away portion of FIG. 3A) thatextends about a perimeter edge 2000 of blanket 200, and within perimeteredge 2000 to form zones, or pockets, where a gap exists between the twosheets.

FIG. 3A further illustrates flaps 25 including zones where there aregaps between the sheets to enclose weighting members, which are shown asrelatively flat plastic slabs 255. Alternately flaps 25 can be weightedby attaching weighting members to exterior surfaces thereof.

FIG. 3C is a top plan view, including partial cut-away views, of heatingelement assembly 250′, which may be incorporated in blanket 200; andFIG. 3D is a cross-section view through section line D-D of FIG. 3C.FIGS. 3C-D illustrates heating element assembly 250′ including heatingelement 10 overlaid with electrical insulation 210 on both sides 13, 14and thermal insulation layer 201 extending over the top side 14 thereof(dashed lines show leads and sensor assembly beneath layer 201).According to the illustrated embodiment, layer 201 is inserted beneath aportion of each insulating member 18, each which has been folded overthe respective bus bar 15, for example as illustrated by arrow B in FIG.1C, and then held in place by a respective row of non-conductivestitching 345 that extends through member 18, layer 201 and heatingelement 10. Although layer 210 is shown extending beneath layer 201 onside 14 of heating element, according to alternate embodiments, layer201 independently performs as a thermal and electrical insulation sothat layer 210 is not required on side 14 of heating element 10.

Returning now to FIG. 2A, to be referenced in conjunction with FIGS.3A-C, connector housing 225 and connector 23 will be described ingreater detail. According to certain embodiments, housing 225 is aninjection molded thermoplastic, for example, PVC, and may be coupled toassembly 250 by being stitched into place, over insulating layer 210.FIG. 2A shows housing 225 including a flange 253 through which suchstitching can extend. With reference to FIGS. 3A-B, it can be seen thatconnector 23 protrudes from shell 20 of blanket 200 so that an extensioncable 330 may couple bus bars 15 to a power source 234, and temperaturesensor assembly 421 to a temperature controller 232, both shownincorporated into a console 333. In certain embodiments, power source234 supplies a pulse-width-modulated voltage to bus bars 15. Thecontroller 232 may function to interrupt such power supply (e.g., in anover-temperature condition) or to modify the duty cycle to control theheating element temperature. According to the illustrated embodiment, asurface 252 of flange 253 of housing 225 protrudes through a hole formedin thermal insulating layer 201 (FIG. 3C) so that a seal 202 (FIG. 3A)may be formed, for example, by adhesive bonding and/or heat sealing,between an inner surface of shell 20 and surface 252.

FIGS. 3C-D further illustrate a pair of securing strips 217, eachextending laterally from and alongside respective lateral portions 11,12 of heating element 10 and each coupled to side 13 of heating element10 by the respective row of stitching 345. Another pair of securingstrips 271 is shown in FIG. 3C, each strip 271 extending longitudinallyfrom and alongside respective ends 101, 102 of heating element 10 andbeing coupled thereto by a respective row of non-conductive stitching354. Strips 217 preferably extend over conductive stitching 145 on side13 of heating element 10, as shown, to provide a layer of insulationthat can prevent shorting between portions of side 13 of heating element10 if element 10 were to fold over on itself along rows of conductivestitching 145 that couple bus bars 15 to heating element 10; however,strips 217 may alternately extend over insulating member 18 on theopposite side of heating element 10. According to the illustratedembodiment, securing strips 217 and 271 are made of a polymer material,for example polyurethane, so that they may be heat sealed between thesheets of shell 20 in corresponding areas of heat seal zone 22 in orderto secure heating element assembly 250′ within the corresponding gapbetween the two sheets of shell 20 (FIG. 3A).

FIG. 4A is a plan view of flexible heating element 30, according to somealternate embodiments of the present invention. Heating element 30 issimilar in nature to previously described embodiments of heating element10, being comprised of a conductive fabric, or a fabric incorporatingclosely spaced conductive elements, for a substantially uniform wattdensity output, preferably less than approximately 0.5 watts/sq. inch.While a shape of the surface area of heating element 10 is suited for alower body blanket, such as blanket 200, that would cover a lowerabdomen and legs of a patient (FIG. 3B) undergoing upper body surgery,the shape of a surface area of heating element 30 is suited for an upperbody heating blanket, for example, blanket 300 shown in FIG. 4C, thatwould cover outstretched arms and a chest area of a patient undergoinglower body surgery (FIG. 4D). With reference to FIG. 4B, which showsheating element 30 incorporated into a heating element assembly 450, itcan be seen that bus bars 15 are coupled to element 30 alongsiderespective lateral edges 311, 312 (FIG. 4A).

FIG. 4B is a top plan view, including partial cut-away views, of heatingelement assembly 450, according to some embodiments of the presentinvention, which may be incorporated in blanket 300 shown in FIG. 4C.FIG. 4B illustrates assembly 450 having a configuration similar to thatof assembly 250′, which is illustrated in FIGS. 3C-D. According to theembodiment illustrated in FIG. 4B, temperature sensor assembly 421 iscoupled to heating element 30 at a location where element 30, whenincorporated in an upper body heating blanket, for example, blanket 300,would come into conductive contact with the chest of a patient, forexample as illustrated in FIG. 4D, in order to maintain a safetemperature distribution across element 30; bus bar junctions 50 andconnector housing 225 are located in proximity to sensor assembly 421 inorder to keep a length of leads 205 and 221 to a minimum. With referenceback to FIGS. 3C-D, in conjunction with FIG. 4B, an electricalinsulating layer 310 of assembly 450 corresponds to insulating layers210 of assembly 250′, a thermal insulating layer 301 of assembly 450corresponds to layer 201 of assembly 250′, and securing strips 317 and371 of assembly 450 generally correspond to strips 217 and 271,respectively, of assembly 250′.

FIG. 4C is a top plan view, including partial cut-away views, of upperbody heating blanket 300, according to some embodiments of the presentinvention. FIG. 4C illustrates blanket 300 including heating elementassembly 450 covered by a flexible shell 40; shell 40 protects andisolates assembly 450 from an external environment of blanket 300 andmay further protect a patient disposed beneath blanket 300 fromelectrical shock hazards. According to the illustrated embodiment, shell40, like shell 20, includes top and bottom sheets; the sheets extendover either side of assembly 450 and are coupled together along a sealzone 32 that extends around a perimeter edge 4000 and within edge 4000to form various zones, or pockets, where gaps exist between the twosheets. The sheets of shell 40 may be heat sealed together along zone32, as previously described for the sheets of shell 20. With referenceto FIG. 4B, securing strips 317 may be heat sealed between the sheets ofshell 40 in corresponding areas of seal zone 32, on either side of acentral narrowed portion 39 of blanket 300, in order to secure heatingelement assembly 450 within the corresponding gap between the two sheetsof shell 40. According to an alternate embodiment, for example, as shownwith dashed lines in FIG. 4A, lateral edges 311, 312 of heating element30 extend out to form securing edges 27 that each include slots or holes207 extending therethrough so that inner surfaces of sheets of shell 40can contact one another to be sealed together and thereby hold edges 27.It should be noted that either of blankets 200, 300, according toalternate embodiments of the present invention, may include more thanone heating element 10, 30 and more than one assembly 250/250′, 450.

With reference to FIG. 4C, it may be appreciated that blanket 300 issymmetrical about a central axis 30 and about another central axis,which is orthogonal to axis 30. FIG. 4C illustrates shell 40 formingflaps 35A, 35B and 350, each of which having a mirrored counterpartacross central axis 30 and across the central axis orthogonal to axis30. According to the illustrated embodiment, each of flaps 35A, Binclude weighting members 305, which are similar to members 255 ofblanket 200, and which may stiffen flaps 35A,B (dashed lines indicateoutlines of members 305 held between the sheets of cover 40 bysurrounding areas of seal zone 32).

FIG. 4C further illustrates straps 38, each extending between respectiveflaps 35A-B. With reference to FIG. 4D, which is a schematic end view ofblanket 300 draped over an upper body portion of a patient, it may beappreciated that flaps 35A-B and 350 extend downward to enclose theoutstretched arms of the patient in order to prevent heat loss and thatstraps 38 secure blanket 300 about the patient.

With further reference to FIG. 4D, it may also be appreciated that, whenblanket 300 is positioned over the patient, each strap 38 is positionedin proximity to an elbow of the patient so that either end portion ofblanket 300, corresponding to each pair of flaps 35A, may be temporarilyfolded back, as illustrated, per arrow C, in order for a clinician toaccess the patient's arm, for example, to insert or adjust an IV.According to some embodiments of the present invention, superover-temperature sensors, for example, sensors 41, previously described,are included in blanket 300 being located according to the anticipatedfolds, for example at general locations 410 illustrated in FIGS. 4B-C,in order to detect over-heating, which may occur if blanket 300 isfolded over on itself, as illustrated in FIG. 4D, for too long a time,and, particularly, if flaps 35A of folded-back portion of blanket areallowed to extend downward as illustrated with the dashed line in FIG.4D. FIG. 4D further illustrates connector cord 330 plugged intoconnector 23 to couple heating element 30 and temperature sensorassembly 421 of blanket 300 to control console 333.

In the foregoing detailed description, the invention has been describedwith reference to specific embodiments. However, it may be appreciatedthat various modifications and changes can be made without departingfrom the scope of the invention as set forth in the appended claims.Although embodiments of the invention are described in the context of ahospital operating room, it is contemplated that some embodiments of theinvention may be used in other environments. Those embodiments of thepresent invention, which are not intended for use in an operatingenvironment and need not meet stringent FDA requirements for repeatedused in an operating environment, need not including particular featuresdescribed herein, for example, related to precise temperature control.Thus, some of the features of preferred embodiments described herein arenot necessarily included in preferred embodiments of the invention whichare intended for alternative uses.

1. An electric warming blanket for warming patients during surgery andother medical procedures, comprising: a flexible heater having a surfacearea and a substantially uniform watt density output across the surfacearea when the heater is electrically powered; a temperature sensorassembly coupled to the heater and providing input of an averagetemperature over a portion of the surface area of the heater to atemperature controller when the heater and the sensor assembly arecoupled to the controller; and a first layer of water resistant materialcoupled to a second layer of water resistant material about a perimeterof the heater to form a substantially hermetically sealed space for theheater and the temperature sensor assembly.
 2. The blanket of claim 1,wherein the heater comprises a conductive fabric.
 3. The blanket ofclaim 1, wherein the heater comprises carbon.
 4. The blanket of claim 1,wherein the heater comprises a nonconductive layer coated with aconductive material.
 5. The blanket of claim 4, wherein thenonconductive layer comprises a woven polyester and the conductivematerial comprises polypyrrole.
 6. The blanket of claim 1, wherein theheater comprises a fabric incorporating closely spaced conductiveelements.
 7. The blanket of claim 1, wherein the portion is disposedalong the surface area so at to be in conductive contact with thepatient when the blanket is placed over the patient to warm the patient.8. The blanket of claim 1, wherein the temperature sensor assemblyincludes a temperature sensor coupled to a heat spreader, the heatspreader extending over the portion of the surface area.
 9. The blanketof claim 8, wherein the portion of the surface area is no greater thanapproximately four square inches.
 10. The blanket of claim of claim 8,wherein the heat spreader comprises a metal foil.
 11. The blanket ofclaim 1, wherein the temperature sensor assembly includes a distributedtemperature sensor comprising a resistance temperature detector (RTD)laid out in a flat plane across the portion of the surface area.
 12. Theblanket of claim 1, wherein the temperature sensor assembly includes anarray of temperature sensors spaced apart over the portion of thesurface area.
 13. An electric warming blanket for warming patientsduring surgery and other medical procedures, comprising: a flexibleheater including a first side and a second side, at least one of thefirst and second sides having a surface area and a substantially uniformwatt density output across the surface area when the heater iselectrically powered; a temperature sensor assembly coupled to the firstside of the heater; a first layer of water resistant material disposedover the first side of the heater, being un-adhered thereto, and forminga top surface of the blanket when the blanket is placed over thepatient; a second layer of water resistant material disposed over thesecond side of the heater, being un-adhered thereto, and forming abottom surface of the blanket, adjacent to the patient, when the blanketis placed over the patient, the first layer of water resistant materialcoupled to the second layer of water resistant material about aperimeter of the heater to form a substantially hermetically sealedspace for the heater and the temperature sensor; and a layer of thermalinsulation disposed between the temperature sensor assembly and thefirst layer of water resistant material.
 14. The blanket of claim 13,wherein the flexible heater comprises a conductive fabric.
 15. Theblanket of claim 13, wherein the heater comprises carbon.
 16. Theblanket of claim 13, wherein the heater comprises a nonconductive layercoated with a conductive material.
 17. The blanket of claim 16, whereinthe nonconductive layer comprises a woven polyester and the conductivematerial comprises polypyrrole.
 18. The blanket of claim 13, wherein theflexible heater comprises a fabric incorporating closely spacedconductive elements.
 19. The blanket of claim 13, wherein the layer ofthermal insulation comprises flexible polymeric foam.
 20. The blanket ofclaim 13, wherein the layer of thermal insulation comprises high loftfibrous polymeric non-woven material.
 21. The blanket of claim 13,wherein the layer of thermal insulation comprises non-woven cellulosematerial.
 22. The blanket of claim 13, wherein the layer of thermalinsulation comprises air.
 23. An electric warming blanket for warmingpatients during surgery and other medical procedures, comprising: aflexible heater having a surface area and a substantially uniform wattdensity output across the surface area when the heater is electricallypowered; and a temperature sensor assembly coupled to the heater, thesensor assembly including a temperature sensor and a heat spreader, andthe heat spreader comprising a metal foil disposed between thetemperature sensor and the heater.
 24. The blanket of claim 23, whereinthe temperature sensor comprises a surface mount chip thermistor. 25.The blanket of claim 23, wherein the heat spreader extends over aportion of the surface area of the heater, the portion being no greaterthan approximately four square inches.
 26. The blanket of claim 23wherein the heater spreader has a thickness that is no greater thanapproximately 0.001 inch.